Maybe considered as the weighted average maturity of a bond's cash flows or of any series of linked cash flows. At one extreme are zero coupon bonds, whose duration is equal to the bond’s term to maturity, because there are no cash flows to weight until the redemption payment at the maturity date. For bonds that make intermittent coupon payments, the duration will be less than the bond’s term to maturity. This measure is closely related to the first derivative of the bond's price function with respect to the interest rate. Portfolio investors consider the duration to be this measure of price sensitivity to interest-rate changes, with the weighted average maturity simply being an easy method of calculating the duration for a non-callable bond. Sometimes explained inaccurately as a measure of how long, in years, it takes for the price of a bond to be repaid by its internal cash flows.